/*
 * Usurpataion --- clinet-server protocol implementation.
 *
 * Copyright (C) 2019 Ramūnas Mažeikis
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; version 2.1
 * of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include "protocol.h"
#include "protocol_private.h"
#include "net.h"
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define READ_AS(from, type)	(*(type*)(from))

#define GET_MSG_CHAR(i)		(msg_buf[(i) % MSG_BUF_SIZE])
#define SET_MSG_CHAR(i, ch)	msg_buf[(i) % MSG_BUF_SIZE] = (ch)

/* Increment message cursor */
#define IMC(x)	((msg_cursor + (x)) % MSG_BUF_SIZE)

/* Begins at 2 because this way we'll have two null's at the beggining
 * indicating that going back is not possible.
 * */
static int msg_cursor = 2;
/* Two consecutive null's indicate that going back is not possible.
 * */
static char msg_buf[MSG_BUF_SIZE] = {0};

static int tlv_cursor = 0;
static struct tlv tlv_buf[TLV_BUF_SIZE] = {0};

static size_t packet_cursor = 0;
/* Outgoing packet.
 * */
static char packet_buf[PACKET_MAX_SIZE] = {0};

static int push_bytes(const void * const data, const size_t size)
{
	if (packet_cursor + size >= PACKET_MAX_SIZE) {
		return E_PACKET_OVERFLOW;
	}
	memcpy(packet_buf + packet_cursor, data, size);
	packet_cursor += size;
	return 0;
}

void clear_data(void)
{
	packet_cursor = 0;
}

int push_data(const char *data, enum tlv_type type)
{
	int ret = E_UNKNOWN_TYPE;
	switch (type) {
	case TEXT:
		ret = push_string(data);
		break;
	case FPI1:
		ret = push_fpi1(data);
		break;
	case TIMESTAMP:
		ret = push_timestamp(data);
		break;
	case REQUEST:
		ret = push_request(data);
		break;
	case REPLY:
		ret = push_reply(data);
		break;
	case UUID:
		ret = push_uuid(data);
		break;
	}
	return ret;
}

static int push_string(char *str)
{
	size_t size = strlen(str);

	push_tlv_header(TEXT, size);
	push_bytes(str, size);
	return 0;
}

static int push_fpi1(char *num)
{
	return		push_tlv_header(FPI1, sizeof(fpi1_t))
		|	push_bytes(num, sizeof(fpi1_t));
}

static int push_timestamp(char *data)
{
	return		push_tlv_header(TIMESTAMP, sizeof(time_t))
		|	push_bytes(data, sizeof(time_t));
}

static int push_request(char *data)
{
        return          push_tlv_header(REQUEST, sizeof(msg_idx_t))
                |       push_bytes(data, sizeof(msg_idx_t));
}

static int push_reply(char *data)
{
        int ret = 0;
        size_t msglen = strlen(data + sizeof(msg_idx_t));
        ret |= push_tlv_header(REPLY, msglen + sizeof(msg_idx_t));
        ret |= push_bytes(data, msglen);
        return ret;
}

static int push_uuid(char *data)
{
	return		push_tlv_header(UUID, sizeof(uuid_t))
		|	push_bytes(data, sizeof(uuid_t));
}

static int push_tlv_header(enum tlv_type type, size_t size)
{
	if (size + sizeof(type) + packet_cursor >= PACKET_MAX_SIZE) {
		return E_PACKET_OVERFLOW;
	}
	READ_AS(packet_buf, enum tlv_type) = type;
	packet_cursor += sizeof(type);
	READ_AS(packet_buf, size_t) = size;
	packet_cursor += sizeof(size);
	return 0;
}

void get_last_data()
{
	msg_cursor = 2;
	msg_buf[0] = '\0';
	msg_buf[1] = '\0';
	tlv_cursor = 0;
	get_tlvs(packet_buf, tlv_buf, TLV_BUF_SIZE);
}

struct tlv * get_tlv(void)
{
	struct tlv *ret;
	if (tlv_buf + tlv_cursor != NULL) {
		struct tlv *ret = &tlv_buf[tlv_cursor++];
	} else {
		ret = NULL;
	}
	return ret;
}

size_t tlv_count(const struct packet_data * const packet)
{
	size_t cursor = 0;
	size_t length = 0;
	size_t ret = 0;

	while (cursor < packet->packet_size) {
		cursor += sizeof(enum tlv_type);
		length = READ_AS(packet->data + cursor, enum tlv_type);
		cursor += sizeof(size_t) + length;
		ret++;
	}
	if (cursor != packet->packet_size) {
		errno = E_TLV_OVERFLOW;
	}
	return ret;
}

size_t get_tlvs(	const struct packet_data * const data,
			const struct tlv *buf,
			size_t buf_size)
{
	size_t tlvs_read = 0;
	size_t cursor = 0;

	while (cursor < data->packet_size && tlvs_read <= buf_size) {
		cursor += parse_tlv(data->data, cursor, buf + tlvs_read);
		tlvs_read++;
	}

	if (cursor > data->packet_size) {
		errno = E_TLV_OVERFLOW;
	}

	return tlvs_read;
}

size_t parse_tlv(char *data, size_t cursor, struct tlv *t)
{
	char *begin = data + cursor;

	t->type = READ_TLV_TYPE(data + cursor);
	cursor += sizeof(enum tlv_type);
	t->length += READ_SIZE_T(data + cursor);
	data += sizeof(size_t);
	t->data = data + cursor;

	return data + cursor - begin + 1UL;
}